In mice with the brain development disorder, a bone marrow transplant reduced the disease's symptoms, a new study shows.
The findings raise treatment possibilities for Rett syndrome, an autism spectrum disorder associated with reduced growth, irregular breathing, and impaired coordination and movement. Some children with the disease don’t learn to speak.
The disorder is caused by mutations of the MECP2 gene on the X chromosome. Because males have only one X chromosome, boys born with the mutation die within weeks of birth. Girls with one faulty copy develop Rett syndrome.
So, a team led by Jonathan Kipnis from the University of Virginia decided to examine the role of one of these non-neuronal brain cells – microglia – in mice models of Rett syndrome, or Mecp2-lacking mice.
Microglia (pictured) are the brain’s macrophages, Nature explains, a type of immune cell that sops up the detritus created by other cells.
- They exposed 4-week-old mice to radiation to kill off their immune cells, including microglia.
- Then they injected the Rett mice with bone marrow cells from ‘normal’ mice with a working copy of Mecp2.
- The transplant caused an invasion of microglia cells expressing normal Mecp2.
Bone marrow gives rise to all cells of the immune system, Science explains, so this treatment essentially gave the mutant mice a brand new immune system that was genetically normal.
Kipnis speculates that microglia from Rett mice have trouble clearing cellular rubbish in the brain, making it more difficult for their neurons to work properly.
The treatment reduced disease symptoms – they breathed easier, walked better, and gained some weight – and increased the lifespan of the Rett mice… even the male ones.
The findings could result in clinical trials of bone marrow transplants or drugs that improve microglia function.
And the immune system is a particularly appealing target for disease treatment because it’s “much more feasible to target than any other target so far,” Kipnis tells The Scientist. “You don’t have to deal with the brain and delivering drugs across the blood-brain barrier.”
However, he also cautions: "It works fantastically in mice, but we can cure almost anything in mice."
The study was published in Nature yesterday.
Image from Derecki et al.